Electric discharge generator and power supply device of electric discharge generator

ABSTRACT

An electric discharge generator and power supply device of electric discharge generator includes a radical gas generation apparatus, a process chamber apparatus, and an n-phase inverter power supply device. The radical gas generation apparatus is located adjacent to the process chamber apparatus. The radical gas generation apparatus includes a plurality of (n) discharge cells. The n-phase inverter power supply device includes a power supply circuit configuration offering a means to control output of n-phase alternating current voltages and variably controls, according to positions of the plurality of discharge cells, the alternating current voltages of different phases.

TECHNICAL FIELD

The present invention relates to an electric discharge generator thatincludes a power supply device, can generate a radical gas, and canperform a process in which the radical gas is used, and also relates toa power supply device of electric discharge generator. The presentinvention is applicable to, for example, formation of a high-performancefilm on a target object.

BACKGROUND ART

In various industries including the semiconductor manufacturing, a needexists for multifunctional, high-quality thin films (e.g., highlyinsulative thin films, semiconductor thin films, highly dielectric thinfilms, light-emitting thin films, highly magnetic thin films, andsuperhard thin films).

For example, in the manufacturing of semiconductor devices, films foruse in semiconductor chips include a highly conductive film with a lowimpedance that corresponds to circuit wiring, a highly magnetic filmthat functions as a wiring coil of a circuit or as a magnet, a highlydielectric film that functions as a capacitor in a circuit, and a highlyinsulative film that causes a less amount of electrical leakage current.

Examples of techniques that have been used to form these films includethe thermal chemical vapor deposition (CVD) apparatus, the photo CVDapparatus, and the plasma CVD apparatus. Particularly, the plasma CVDapparatus has been commonly used. As compared to the thermal and photoCVD apparatuses or the like, the plasma CVD apparatus can lower thetemperature of film formation and increase the speed of film formation,so that a film formation process can be accelerated.

For example, the following technique that uses the plasma CVD apparatusis generally employed to form, on a semiconductor substrate, a gateinsulation film such as a nitride film (e.g., SiON or HfSiON) or anoxide film (SiO₂ or Hfo₂).

Thus, a gas of NH₃ (ammonia), N₃, O₂, O₃ (ozone), or the like and aprecursor gas of silicon, hafnium, or the like are directly supplied toa process chamber apparatus in which the CVD process is to be performed.In the process chamber apparatus, the precursor gas is dissociated toform metal particles, and then, a thin film such as a nitride film or anoxide film is formed on a target object by a chemical reaction betweenthe metal particles and the above-mentioned gas of NH₃ (ammonia) or thelike.

In the plasma CVD apparatus, high-frequency plasma or microwave plasmais directly generated in the process chamber apparatus. The targetobject is accordingly exposed to a radical gas or plasma ions (orelectrons) having a high energy.

Patent document 1 is an example of related art documents in whichtechniques associated with plasma CVD apparatuses are disclosed.

In the film formation process performed in the plasma CVD apparatus, thetarget object is directly exposed to plasma, as mentioned above. Thetarget object is heavily damaged by plasma (ions or electrons), so thatthe performance of a semiconductor function suffers.

In contrast, in the film formation process using the thermal and photoCVD apparatuses, the target object is not damaged by plasma (ions orelectrons), and a high-quality film such as a nitride film or oxide filmis formed accordingly. In such a film formation process, however, it isdifficult to provide a large amount of highly concentrated radical gassource and it accordingly takes a very long time to form a film.

The recent thermal and photo CVD apparatuses use, as a source gas, an HNgas or a O₃ gas, which is highly concentrated and readily dissociated byradiation of heat or light. In a CVD chamber apparatus, a thermalcatalyst is provided. Thus, a catalytic action promotes dissociation ofthe gas in the thermal and photo CVD apparatus, whereby a film such as anitride film or an oxide film can be formed in a short time. However.this saves only a limited amount of time, and thus, it is difficult toaccelerate the film formation significantly.

An example of apparatuses that can reduce damages to the target objectcaused by plasma and can further accelerate the film formation is a filmformation process apparatus of remote plasma type (see, for example,Patent Document 2).

According to the technique disclosed in Patent Document 2, a plasmageneration region and a target object process region arc separated by apartition (plasma confining electrode). Specifically. according to thetechnique disclosed in Patent Document 2, the plasma confining electrodeis located between a high-frequency application electrode and a counterelectrode on which a target object is placed. The technique disclosed inPatent Document 2 provides the target object with only neutral activatedspecies.

According to the technique disclosed in Patent Document 3, part of asource gas is activated by plasma in a remote plasma source. In theremote plasma source, a gas channel circles around in a loop. An activegas generated in the remote plasma source is discharged and supplied tothe apparatus in which a target object is placed.

Various source gases such as a nitrogen gas, an oxygen gas, an ozonegas, or a hydrogen gas may be used in the thin film technique accordingto Patent Document 3 and the like. An activated radical gas is generatedfrom the source gas, and then, a thin film is formed on a target objectthrough the use of the radical gas.

The radical gas is highly reactive. The radical gas in minute quantities(at a concentration less than or equal to about 1%: 1000 ppm) is sprayedonto a target object to promote a chemical reaction in the targetobject, whereby a film such as a nitrogen thin film, an oxide thin film,or a hydrogen-bonding thin film can be efficiently formed in a shorttime.

A radical gas generation apparatus includes discharge cells(generators). In the discharge cells, high-field plasma is createdthrough the use of a dielectric barrier discharge, which is atmosphericpressure plasma. Consequently, a high-quality radical gas is generatedfrom the source gas exposed to the plasma in the discharge cells. Theplurality of discharge cells are disposed in the radical gas generationapparatus, so that the generated radical gas is sprayed in manydifferent quarters and the resultant radical gas becomes available foruse.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent Application Laid-Open No. 2007-266489

Patent Document 2: Japanese Patent Application Laid-Open No. 2001-135628

Patent Document 3: Japanese Patent Application Laid-Open No. 2004-111739

SUMMARY OF INVENTION Problems to be Solved by the Invention

However, the conventional radical gas generation apparatuses fail togenerate an effective, highly reactive radical gas. Further, it isdifficult to obtain a radical gas in large quantities and the radicalgas is supplied from one direction. In addition, the lifetime of thegenerated radical gas is very short. Thus, it is difficult to minimize adecrease in concentration and to conduct a radical from the radical gasgeneration apparatus to a radical gas process area (a thin filmgeneration area, namely, a process chamber apparatus) that is separatefrom the radical gas generation apparatus.

The radical gas outlet may be formed into an orifice such that a radicalgas sprayed from the radical gas generation apparatus is applied to anobject placed in the process chamber apparatus in a short time. Thisinvolves reducing the opening diameter of an opening which is a radicalgas transmission path from the radical gas generation apparatus to theprocess chamber apparatus. Thus, reducing the pressure (creating avacuum) in the process chamber apparatus causes a difference in pressurebetween the inside of the radical gas generation apparatus and theinside of the process chamber apparatus, so that the radical gas issprayed into the process chamber apparatus at a high speed. The radicalgas can be conducted from the radical gas generation apparatus to theprocess chamber apparatus while being kept in high concentrations.

According to the above-mentioned method, the opening needs to have adiameter of, for example, about several tens of millimeters.Unfortunately, through the opening of this size, the radical gas issprayed onto only a limited part of the target object in the processchamber apparatus. This makes it difficult to form a thin film evenly ona large area (e.g., a target object having a diameter of 200 mm ormore).

The present invention therefore has an object to provide a radical gasgeneration system (a film formation process system of remote plasmatype, an electric discharge generator, and a power supply device ofelectric discharge generator) that includes a radical gas generationapparatus and a process chamber apparatus located apart from or adjacentto each other. The electric discharge generator and the power supplydevice of electric discharge generator are capable of conducting aradical gas from the radical gas generation apparatus to the processchamber apparatus, spraying a radical gas in any desired concentrationfrom another quarter into the process chamber apparatus, performing aprocess through the use of the radical gas evenly on, for example, atarget object having a large area, and performing, at a high speed, theprocess in which the radical gas is used.

Means to Solve the Problems

In order to achieve the above-mentioned objective, an electric dischargegenerator and a power supply device of electric discharge generatoraccording to the present invention includes a radical gas generationapparatus, a process chamber apparatus, and a power supply device thatapplies an alternating current voltage to the radical gas generationapparatus. The radical gas generation apparatus generates a radical gasfrom a source gas using a dielectric barrier discharge. The processchamber apparatus is connected to the radical gas generation apparatus,accommodates a target object, and performs, on the target object, aprocess in which the radical gas is used. The process chamber apparatusincludes a table on which the target object is placed. The table causesthe target object to rotate. The radical gas generation apparatusincludes a plurality of discharge cells and a source gas supply unit.The plurality of discharge cells cause the dielectric barrier discharge.The source gas supply unit supplies the radical gas generation apparatuswith the source gas. Each of the plurality of discharge cells includes afirst electrode portion, a second electrode portion, and an opening. Thefirst electrode portion includes a first electrode member. The secondelectrode portion is opposed to the first electrode and includes asecond electrode member. The opening is connected to the inside of theprocess chamber and faces the target object placed on the table. Theradical gas generated from the source gas using the dielectric barrierdischarge is output through the opening. The power supply deviceincludes a power supply circuit configuration that receives input of onealternating current voltage and controls output of n-phase alternatingcurrent voltages, applies each of the n-phase alternating currentvoltages to corresponding one of the plurality of discharge cells, andvariably controls, according to positions of the plurality of dischargecells, the alternating current voltages to be applied to the pluralityof discharge cells, where 11 represents the number of the plurality ofdischarge cells.

Effects of the Invention

The electric discharge generator and the power supply device of electricdischarge generator according to the present invention includes theradical gas generation apparatus, the process chamber apparatus, and thepower supply device that applies the alternating current voltage to theradical gas generation apparatus. The radical gas generation apparatusgenerates the radical gas from the source gas using the dielectricbarrier discharge. The process chamber apparatus is connected to theradical gas generation apparatus, accommodates the target object, andperforms, on the target object, the process in which the radical gas isused. The process chamber apparatus includes the table on which thetarget object is placed. The table causes the target object to rotate.The radical gas generation apparatus includes the plurality of dischargecells and the source gas supply unit. The plurality of discharge cellscause the dielectric barrier discharge. The source gas supply unitsupplies the radical gas generation apparatus with the source gas. Eachof the plurality of discharge cells includes the first electrodeportion, the second electrode portion, and the opening. The firstelectrode portion includes the first electrode member. The secondelectrode portion is opposed to the first electrode and includes thesecond electrode member. The opening is connected to the inside of theprocess chamber and faces the target object placed on the table. Theradical gas generated from the source gas using the dielectric barrierdischarge is output through the opening. The power supply deviceincludes the power supply circuit configuration that receives input ofone alternating current voltage and controls the output of the n-phasealternating current voltages, applies each of the n-phase alternatingcurrent voltages to the corresponding one of the plurality of dischargecells, and variably controls, according to the positions of theplurality of discharge cells, the alternating current voltages to beapplied to the plurality of discharge cells, where n represents thenumber of the plurality of discharge cells.

The radical gas can be conducted from the radical gas generationapparatus to the process chamber apparatus. Also, the small-footprintapparatus can perform, at a low cost, a radical gas process evenly on atarget object having a large area.

Thus, a plurality of radical gases can be conducted from the radical gasgeneration apparatus to the process chamber apparatus. Furthermore, onlyone alternating current power supply is required for the plurality ofdischarge cells to output the radical gas generated at a given flow rateand to conduct the radical gas to the process chamber apparatus. In theradical generation system according to the present invention, the smallradical gas generation apparatus can perform the radical gas processevenly on a target object having a large area in a relatively short timeat a low cost.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 A diagram illustrating an example configuration of a radicalgeneration system 500 according to the present invention.

FIG. 2 An enlarged cross-sectional view of an example configuration of adischarge cell 70 according to the present invention.

FIG. 3 A diagram illustrating drive pulse cycles for use in the drivingof inverter elements 902, pulse-width signal waveforms, and waveforms ofalternating current voltages output to the discharge cells 70.

DESCRIPTION OF EMBODIMENT

As mentioned above, the inventors have found the configuration whichallows a plurality of radical gases, which are kept in highconcentrations, to be conducted from a radical gas generation apparatusto a process chamber apparatus through the use of one alternatingcurrent power supply. In this configuration, radical gases are generatedin the discharge space between opposing electrodes and each dischargecell sprays a radical gas from an opening having a small diameter.

The radical gas generation apparatus and the process chamber apparatusvertically adjoin each other in such a manner that the radical gasgeneration apparatus is stacked on top of the process chamber apparatus.The opening is a radical gas transmission path from the radical gasgeneration apparatus to the process chamber apparatus. A plurality ofopenings are provided. The individual openings face the main surface ofa target object.

In this configuration, however, it is difficult to perform a process inwhich the radical gas is used (hereinafter also referred to as, forexample, a “film formation process”) evenly on the target object placedin the process chamber apparatus, as mentioned above. Increasing thenumber of openings can smooth the unevenness to some extent but fails toeliminate the problem of the unevenness.

As a workaround to the uneven film formation mentioned above, the targetobject is rotated in the process chamber in a plan view. In thisconfiguration, however, the local rotation speed of the target objectincreases with increasing distance from the center of rotation in aplanar direction (v (speed)=r (radius)×ω(angular velocity)). It isdifficult to completely solve the above-mentioned problem of the unevenfilm formation process by the configuration in which the target objectis rotated and the radical gas is sprayed into the process chamberthrough the individual openings.

The following configuration may be another workaround to the uneven filmformation. As mentioned above, the plurality of openings, which areradical spraying portions, are provided. In this configuration,discharge cells are provided in one-to-one correspondence with theopenings and the individual discharge cells control the amount ofgenerated radical gas (the concentration of radical gas).

Each discharge cell may include an alternating current power supply andcontrol (change) the electric power supplied from the alternatingcurrent power supply, so that the amount of radical gas (theconcentration of the radical gas) varies among the discharge cells. Thismethod requires a plurality of alternating current power sources. Thisleads to upsizing of the radical gas generation system as a whole, thusdriving up costs.

Alternatively, the opening diameter of each opening (the aperturediameter of each orifice) may be changed such that the amount of radicalgas varies among the discharge cells. In the case where the openingdiameter of the opening for the radical gas (the aperture diameter ofthe orifice) varies among the discharge cells, the velocity of flow ofradical gas sprayed from the opening also varies among the dischargecells. A film may not be formed evenly owing to variations in thevelocity of flow of gas.

The inventors have provided an inverter power supply in which the amountof radical gas varies among the discharges cells. In one power supply,which will be described below, inverter elements are configured tooutput alternating current voltages of n phases, which are independentof one another. The frequencies of the output n-phase alternatingcurrent voltages are fixed. For each phase, only an amplitude value Ecan be set at any desired value. The power supply is referred to as ann-phase inverter power supply device. The present invention will bespecifically described below with reference to drawings illustrating anembodiment thereof.

Embodiment

FIG. 1 illustrates an example configuration of a radical gas generationsystem 500 including a power supply device (an electric dischargegenerator and a power supply device of electric discharge generator)according to an embodiment. FIG. 2 is an enlarged cross-sectional viewof a configuration of a discharge cell 70 according to the presentinvention. FIG. 3 illustrates one embodiment by showing drive pulsecycles, pulse-width signal waveforms, and waveforms of alternatingcurrent voltages output to the discharge cells 70. The pulse cycles arefor use in the driving of inverter elements 902 included in the n-phaseinverter power supply device 9, which offers a means to output “n”output alternating current voltages.

The radical generation system 500 according to the embodiment will bedescribed below with reference to FIGS. 1, 2, and 3.

As illustrated in FIG. 1, the radical gas generation system 500 includesa radical gas generation apparatus 100, a process chamber apparatus 200,and one n-phase inverter power supply device 9 that can output then-phase alternating current voltages, and a vacuum pump 300.

Here, “n” used to refer the n phase is equivalent to “n” representingthe number of discharge cells 70 disposed in the radical gas generationapparatus 100.

The radical gas generation system 500 is a film formation process systemof remote plasma type in which the radical gas generation apparatus 100that generates a radical gas G2 is located separately from the processchamber apparatus 200 that performs, for example, a film formationprocess in which the generated radical gas G2 is used.

As illustrated in FIG. 1, the bottom surface side of the radical gasgeneration apparatus 100 is in contact with the upper surface side ofthe process chamber apparatus 200. As will be described below, theinside of the radical gas generation apparatus 100 is connected to theinside of the process chamber apparatus 200 through an opening 102. Asmentioned above, a plurality of openings 102 are provided.

In the radical gas generation apparatus 100, the radical gas G2 isgenerated from a source gas G1 using the dielectric barrier discharge.The radical gas G2 is generated from part of the source gas G1 formedinto a radical gas due to the dielectric barrier discharge.

As illustrated in FIG. 1, the radical gas generation apparatus 100includes a plurality of discharge cells 70. Specifically, the dischargecells 70 are located on the bottom surface of the radical gas generationapparatus 100.

As illustrated in FIG. 2, each of the discharge cells 70 includes firstelectrode portions 1 and 2 and second electrode portions 5, 31, and 3.The first electrode portions 1 and 2 are opposed to the second electrodeportion 5, 31, and 3 with a predetermined gap therebetween.

Between the first electrode portions 1 and 2 and the second electrodeportions 5, 31, and 3, a discharge space 40 is fowled in which adielectric barrier discharge occurs. At least one spacer 4 is locatedbetween the first electrode portions 1 and 2 and the second electrodeportions 5, 31, and 3 such that the gap length (the distance between thefirst electrode portions 1 and 2 and the second electrode portions 5,31, and 3 in FIG. 2) is kept equal across the discharge space 40.

As illustrated in FIG. 2, the first electrode portions 1 and 2 include alow voltage electrode (which can be regarded as a first electrodemember) 1 and a first dielectric 2.

The low voltage electrode 1 is at the ground potential and is located onthe bottom surface of the radical gas generation apparatus 100. All ofthe discharge cells 70 share one low voltage electrode 1. The firstdielectric 2 is formed on the low voltage electrode 1.

The second electrode portions 5, 31, and 3 include a high voltageelectrode block 5, a high voltage electrode (which can be regarded as asecond electrode member) 31, and a second dielectric 3, respectively.

The high voltage electrode 31 is formed on the second dielectric 3. Thehigh voltage electrode block 5 is located on the high voltage electrode31 so as to be connected thereto. The high voltage electrode block 5 issupplied with a high alternating current voltage. The high voltageelectrode block 5 is electrically connected to the high voltageelectrode 31, so that the high voltage is also applied to the highvoltage electrode 31.

As illustrated in FIG. 1, the openings 102 that functions as orificesare provided in the individual discharge cells 70.

Each of the openings 102 is formed so as to penetrate the firstdielectric 2 and the low voltage electrode 1. The opening 102 is formedin the middle of the first dielectric 2. Through the opening 102, theinside of the radical gas generation apparatus 100 (specifically, thedischarge space 40) is connected with the inside of the process chamberapparatus 200. Thus, the radical gas G2 generated in the discharge space40 is output to the inside of the process chamber apparatus 200 throughthe opening 102. The opening 102 faces the treatment surface of a targetobject 202 placed in the process chamber apparatus 200.

In one embodiment, the individual discharge cell 70 has a disc-shapedoutline or a coaxial conical outline in a plan view. This means that thefirst dielectric 2 and the second dielectric 3 both have disc shapes orconical shapes and are located in parallel with each other or arelocated coaxially so as to be opposed to each other (the high voltageelectrode 31 also has a disc shape or a conical shape). When thedischarge cell 70 is viewed from the above, the periphery of the firstdielectric 2 coincides with the periphery of the second dielectric 3.The individual discharge cell 70 does not necessarily have a disc-shapedoutline or a conical outline in a plan view and may have any shape aslong as the same effects are produced.

The outlines of the discharge cells 70 are of the same shape. Forexample, in the case where the individual discharge cell 70 has a discshaped outline as mentioned above, the size of the outline of thedischarge cell 70 in a plan view is determined by the diameter of thefirst dielectric 2 (and the diameter of the second dielectric 3).

The n-phase inverter power supply device 9 includes a rectifier circuit901, “n” inverter elements 902, “n” current-limiting reactors 903, “n”transformers 904, current detectors 906 that detect current flowingthrough the inverter elements 902, a gate circuit 905 that drives ON-OFFcommand signals from the individual inverter elements 902, and a controlcircuit 907 that controls the n-phase inverter power supply device 9.

With reference to FIG. 1, a commercial three-phase alternating currentvoltage is input to the rectifier circuit 901 of the n-phase inverterpower supply device 9 (the three-phase alternating current voltageaccording to the illustration may be replaced with a single-phasealternating current voltage). The output voltage from the rectifiercircuit 901 is rectified and converted into a direct current voltage.The direct current voltage is applied to a plurality of (“n”) inverterelements 902 arranged in parallel with each other.

The individual inverter element 902 includes two switching elements suchas power transistors placed in series. The gate of the individualswitching element receives, from the gate circuit 905, input of a signalalternating between ON and OFF. The signal is received, and then, theindividual current-limiting reactor 903 receives input of an alternatingcurrent pulse voltage generated due to the switching between ON and OFFof the direct current voltage. The alternating current pulse voltage isinput to the primary side of the individual transformer 904 via theindividual current-limiting reactor 903.

On the primary side of “n” transformers 904, “n” transformers arecoupled through delta connection. A primary voltage input to theindividual transformer causes a secondary-side voltage of the individualtransformer 904 to rise, and then, the resultant high voltage is output.On the secondary side of the transformers 904, Y-connection is formed,with one end of one of “n” transformers 904 and one end of another oneof “n” transformers 904 being integral with each other and being at thesame low voltage (LV). Alternating current high voltages (HV) ofdifferent phases are output to secondary-side terminals, each of whichbeing another end of the individual transformer 904. The alternatingcurrent high voltages (HV) of different phases are applied to thedischarge cells 70.

With reference to FIG. 1, the n-phase inverter power supply device 9 canoutput, to the radical gas generation apparatus 100 (specifically, tothe discharge cells 70), a plurality of alternating current highvoltages for discharging. When the plurality of alternating current highvoltages are applied to the discharge cells 70, a dielectric barrierdischarge occurs in the discharge space 40 of the individual dischargecell 70. Then, the radical gas G2 is generated in the discharge space 40due to the interaction between the source gas G1 passing through thedischarge space 40 and the dielectric barrier discharge. That is to say,the radical gas G2, which is part of the source gas G1 formed into aradical gas due to the dielectric barrier discharge, is generated in theradical gas generation apparatus 100 using the dielectric barrierdischarge.

Provided on the upper surface portion of the radical gas generationapparatus 100 is a source gas supply unit 101. The source gas supplyunit 101 supplies the radical gas generation apparatus 100 with thesource gas G1, from which the radical gas G2 is to be derived. Thesource gas G1 supplied from the source gas supply unit 101 fills theradical gas generation apparatus 100. The fixed amount of the source gasG1 enters the discharge cells 70 from the outside thereof and flowsthrough the discharge spaces 40.

The radical gas G2 generated in the radical gas generation apparatus 100is sprayed into the process chamber apparatus 200. The process chamberapparatus 200 performs a process, such as thin film formation, on themain surface of the target object 202 using the radical gas.

Suppose that the radical gas generation apparatus 100 is supplied withthe source gas G1 which is a nitrogen gas. In this case, a nitrogenradical gas is generated, as the radical gas G2, from the nitrogen gasin the discharge cells 70 of the radical gas generation apparatus 100.The process chamber apparatus 200 accordingly forms a nitride film onthe target object 202 using the nitrogen radical gas G2 sprayed from theradical gas generation apparatus 100.

Suppose that the radical gas generation apparatus 100 is supplied withthe source gas G1 which is an ozone gas or an oxygen gas. In this case,an oxygen radical gas is generated, as the radical gas G2, from theozone gas or the oxide gas in the discharge cells 70 of the radical gasgeneration apparatus 100. The process chamber apparatus 200 accordinglyforms an oxide film on the target object 202 using the radical gas G2sprayed from the radical gas generation apparatus 100.

Suppose that the radical gas generation apparatus 100 is supplied withthe source gas G1 which is a hydrogen gas or water vapor. In this case,a hydrogen radical gas is generated, as the radical gas G2, from thehydrogen gas in the discharge cells 70 of the radical gas generationapparatus 100, or an OH radical gas (a hydroxyl radical gas) isgenerated, as the radical gas G2, from the water vapor in the dischargecells 70 of the radical gas generation apparatus 100. The processchamber apparatus 200 accordingly forms a hydrogen-reduced film (a metalfilm with enhanced hydrogen bonding) on the target object 202 using thehydrogen radical gas G2 or the OH radical gas G2 sprayed from theradical gas generation apparatus 100.

Provided on the lower side surface of the process chamber apparatus 200is a gas outlet 203 that is to be connected to the vacuum pump 300. Thegas is discharged through the vacuum pump 300, so that the pressure inthe process chamber apparatus 200 is maintained at about several tons toseveral tens of tons (several kPa). The vacuum pump 300 produces a flowof gas from the radical gas generation apparatus 100 to the processchamber apparatus 200. The openings 102 function as orifices so that apressure division is provided between the radical gas generationapparatus 100 and the process chamber apparatus 200.

As illustrated in FIG. 1, a table 201 is located in the process chamberapparatus 200. The target object 202 is placed on the table 201. Thetarget object 202 is exposed to the radical gas G2 sprayed from theopenings 102 of the radical gas generation apparatus 100. Then, thetarget object 202 undergoes a process (e.g., formation of a thin film)in which the radical gas G2 is used. The table 201 rotates clockwise orcounterclockwise in a plan view in a state in which the target object202 is placed thereon. The target object 202 accordingly rotates alongwith the table 201.

As mentioned above, the outlines of the discharge cells 70 are of thesame shape. The openings 102 formed in the discharge cells 70 have thesame opening diameter. Thus, the pressure drop caused by a flow of gasbecomes equal among the discharge cells 70 and the openings 102. The gasflows equally through the discharge cells 70, so that the radical gas G2is sprayed into the process chamber apparatus 200 at approximately thesame speed.

As illustrated in FIG. 1, an LV output terminal of the n-phase inverterpower supply device 9 is connected to the low voltage electrode 1through a terminal 8. As mentioned above, the low voltage electrode 1 isshared by the discharge cells 70 and is at the ground potential. HVoutput terminals of the n-phase inverter power supply device 9 areconnected to the high voltage electrode blocks 5 of the discharge cells70 through terminals 7 a, 7 b, . . . , and 7 n. The n-phase inverterpower supply device 9 can apply the n-phase alternating current highvoltages to the discharge cells 70 through the above-mentionedinterconnection.

As mentioned above, one n-phase inverter power supply device 9 applies,to the discharge cells 70, the plurality of alternating current highvoltages (HV) of different phases. The low voltage electrode 1 and thehigh voltage electrode block 5 each include a structure that can providecooling using coolant or the like to dissipate the generated heat. Sucha structure for providing cooling is omitted for the sake of simplifyingthe drawing.

In each discharge cell 70, the discharge space 40 is the region in whichthe high voltage electrode 31 and the low voltage electrode 1 face eachother. The LV output terminal of the n-phase inverter power supplydevice 9 is connected to the low voltage electrode 1, whereas the HVoutput terminals of the n-phase inverter power supply device 9 areconnected to the high voltage electrodes 31 through the terminals 7 a, 7b, . . . , and 7 n, and the high voltage electrode blocks 5. When analternating current high voltage is applied between the low voltageelectrode 1 and the individual high voltage electrode 31, the dielectricbarrier discharge occurs in the individual discharge space 40. Asmentioned above, the radical gas G2, which is part of the source gas G1formed into a radical gas due to the dielectric barrier discharge, isgenerated in the individual discharge space 40 through the use of thesource gas G1 and the dielectric barrier discharge as mentioned above.

Through the openings 102, the generated radical gas G2 is sprayed on thetarget object 202 placed in the process chamber apparatus 200 asmentioned above. The concentration of the radical gas G2 sprayed intothe process chamber apparatus 200 is normally less than 1% (10000 ppm)and most of the remaining gas is the source gas G1. The source gas G1serves as a carrier gas that carries the generated radical gas G2 fromthe discharge cells 70 to the inside of the process chamber apparatus200 in a short time.

Thus, the speed of the radical gas G2 sprayed from the openings 102 ofthe discharge cells 40 is dependent on the source gas G1. When the sprayspeed is low, it takes much time for the radical gas G2 to reach thetarget object 202 and part of the generated radical gas G2 probablydisappears. Consequently, the target object 202 is exposed to theradical gas G2 in small concentrations (gas concentrations). Thistranslates into a reduction in the efficiency of the process performedon the target object 202 through the use of the radical gas G2.

Thus, the speed of the radical gas G2 sprayed from the openings 102 ofthe discharge cells 40 needs to be kept at a certain level or higher. Itis desirable that each of the openings 102 be shaped in an orifice witha small opening diameter.

In the case where each of the openings 102 has a small opening diameter,the radical gas G2 is sprayed at a higher speed, and thus, the radicalgas G2 is less likely to disappear. However, the area of the targetobject 202 exposed to the radical gas G2 is confined within narrowlimits. Although each of the discharge cells 70 has the opening 102formed therein, it is difficult to apply the radical gas G2 evenly tothe target object 202 in the state in which the area exposed to theradical gas G2 is limited within narrow limits.

It is desirable that the spray speed of the radical gas G2 be kept equalamong the discharge cells 70. The discharge cells 70 have the sameoutline shape and the openings 102 have the same opening diameter suchthat the spray speed of the radical gas G2 becomes equal among thedischarge cells 70.

It is undesirable that the spray speed of the radical gas G2 vary amongthe discharge cells 70. Meanwhile, each of the openings 102 needs tohave a small opening diameter such that the radical gas G2 can besprayed at a high speed. However, reducing the opening diameter makes itdifficult to perform the radical gas process evenly over a wide area.

The present invention therefore has the following configuration suchthat the spray speed of the radical gas G2 is kept high and equal amongthe discharge cells 70 and that the radical gas process is performedevenly over a wide area of the target object 202.

When being exposed to the radical gas G2, the target object 202 isrotated along with the table 201 at a certain speed. The radical gasgeneration apparatus 100 includes the plurality of discharge cells 70.Each of the discharge cells 70 has the opening 102. The position of theindividual opening 102 is fixed.

The target object 202 is rotated while the radical gas G2 is sprayedfrom the openings 102, so that the radical gas process can be performedmore extensively on the target object 202. However, the circumferentialspeed varies from position to position, according to the distance fromthe rotation center of the target object 202. In the state where theradical gas G2 is sprayed from the discharge cells 70 at the same rateand the circumferential speed varies from position to position, theperformance of the radical gas process on the target object 202 variesaccording to the distance from the rotation center of the target object202.

Thus, the flow ate of the radical gas G2 sprayed from the dischargecells 70 needs to be changed and adjusted with respect to the rotationcenter of the target object 202. In other words, the flow rate componentof the radical gas G2, which has been formed into a radical and is to besprayed from the discharge cells 70, needs to be controlled inaccordance with the circumferential speed associated with the rotationof the target object 202 (the table 201) such that the radical gasprocess is performed evenly on the target object 202.

In the present invention, the flow rate of the radical gas G2 iscontrolled in such a manner that, of the discharge cells 70, a dischargecell 70 located farther from the center position of the rotation of thetarget object 202 in a plan view is subjected to application of a higheralternating current voltage waveform, which is applied between the highvoltage electrode 31 and the low voltage electrode 1. This voltageapplication increases the load current to be supplied to the dischargespace 40, with increased supply of electric discharge energy to thedischarge cells 70 and increased production of the radical gas G2. Theflow rate component of the radical gas G2 formed into a radical can bechanged according to the position of the individual discharge cell 70.

The circumferential speed is higher at a position farther from therotation center of the target object 202, and thus, such a position isexposed to the radical gas G2 for a shorter period of time. Conversely,the circumferential speed is lower at a position closer to the rotationcenter of the target object 202, and thus, such a position is exposed tothe radical G2 for a longer period of time. Here, the rotation speed(angular speed) of the target object 202 is constant. The value of thealternating current voltage to be applied to the individual dischargecell 70 is changed in such a manner that the amount of the radical gas(the concentration of the radical gas) generated in the discharge cell70 is inversely proportional to the exposure time determined based onthe position of the discharge cell 70.

Take, for example, two discharge cells 70. One discharge cell 70 islocated at a first distance from the rotation center of the targetobject 202 in a plan view. The other discharge cell 70 is located at asecond distance from the rotation center of the target object 202 in aplan view. The first distance is shorter than the second distance.

In this case, the n-phase inverter power supply device 9 applies thealternating current voltage in such a manner that the value of thealternating current voltage applied between the high voltage electrode31 and the low voltage electrode 1 of the other discharge cell 70 ishigher than the value of the alternating current voltage applied betweenthe high voltage electrode 31 and the low voltage electrode 1 of the onedischarge cell 70. Thus, the amount of the electric discharge energyapplied to the other discharge cell 70 becomes greater than the amountof the electric discharge energy applied to the one discharge cell 70,and the amount (concentration) of the radical gas generated due todischarge becomes greater in the other discharge cell 70 than in the onedischarge cell 70, accordingly. Thus, the flow rate component of theradical gas G2 sprayed from the opening 102 of the other discharge cell70 becomes greater than the flow rate component of the radical gas G2sprayed from the opening 102 of the one discharge cell 70.

As mentioned above, the n-phase inverter power supply device 9 appliesalternating current voltages of different values to the discharge cells70 according to the distance between the individual discharge cell 70and the above-mentioned rotation center such that the concentration ofthe radical gas G2 generated in the discharge space 40 varies accordingto the distance between the individual discharge cell 70 and theabove-mentioned rotation center. With reference to FIGS. 1 and 3, thefollowing will describe the configuration and the operation of then-phase inverter power supply device 9 that can apply voltage in theabove-mentioned manner.

In the n-phase inverter power supply device 9 illustrated in FIG. 1, thecommercial alternating current power supply (e.g., a three-phase voltageof 200V at a frequency of 60 Hz) on the input side is converted into adirect current by the rectifier circuit 901, and then, is input to eachof “n” inverter elements 902 connected in parallel with each other. Theinverter elements 902 receive ON-OFF drive signals from the gatecircuits 905, so that each of “n” inverter elements 902 can output agiven pulse voltage. The output pulse voltage is input to the individualtransformer 904 through the individual current-limiting reactor 903. Theindividual transformer 904 boosts the alternating current voltagecorresponding to the pulse voltage input from the individual inverterelement 902. The boosted alternating current high voltage is applied tothe individual discharge cell 70.

When the ON-OFF drive signals a, b, c, d, . . . , and n illustrated inFIG. 3 are input from the gate circuits 905 to the inverter elements902, output units of the transformers 904 can output alternating currentvoltages of different amplitudes (see the waveforms of the n-phasealternating current voltages shown in the lowermost part of FIG. 3).

In the control circuit 907 of the power supply, a pulse cycle T in whicheach signal turns on and off is kept almost constant (an outputfrequency f (=1/T) of the inverter is fixed). The ON cycle (phase) ofeach pulse is moved by the phase (=2·π/n) obtained by dividing a phaseangle of 2π by n. The above-mentioned ON-OFF drive signals arerepresented by pulse signals a, b, c, d, . . . , and n illustrated inFIG. 3.

A pulse width τ of each of the pulse signals a, b, c, d, . . . , and nillustrated in FIG. 3 may be increased in accordance with changes inphase, so that the n-phase alternating current voltages vary inamplitude.

The current detectors 906 detect a current value and the like for eachof the alternating current voltages such that the individual dischargecell 70 can output a predetermined amount of electric discharge energy,regardless of changes in load conditions associated with, for example,the ambient temperature in the individual discharge cell 70, the flowrate of the supplied source gas, the gas pressure in the individualdischarge cell 70, and the pressure in the process chamber. The currentdetectors 906 gives detection result feedback to the control circuit907. In the control circuit 907, the proportional-integral-derivative(PID) control is performed on the set pulse width τ or the set pulsecycle T based on the detection results. This can further stabilize theamount of electric power supplied to each phase.

In the control circuit 907, the PID control is performed on the pulsewidth τ according to the amount by which the feedback current valuediffers from the target current value in each phase. The amount ofelectric power supplied can be accurately controlled per phase throughthe PID control.

The pulse voltage divided into n phases in the inverter elements 902 issupplied to the primary side of the individual transformer 904 throughthe individual current-limiting reactor 903. For example, the deltaconnection or the Y connection is formed on the primary side of theindividual transformer 904 to magnetically couple the primary side tothe secondary winding. The voltage input to the primary side is boostedaccording to the turns ratio between the primary winding and thesecondary winding. The Y connection is desirably formed on the secondaryside of the individual transformer in order to output, from thesecondary side, the common low voltage LV and the high voltages HV ofdifferent phases independent of one another.

With reference to FIG. 2, the spray speed of the radical gas G2 isdetermined based mainly on the outside shapes of the dielectrics 2 and3. As mentioned above, it is desirable that the outlines of thedischarge cells 70 be of the same shape as illustrated in FIG. 2 suchthat the radical gas G2 is sprayed at the same speed. As long as theoutside shapes of the dielectrics 2 and 3 are equal among the dischargecells 70, the radical gas G2 can be sprayed from the discharge cells 70at the same speed, regardless of the differences in the outside shape ofthe high voltage electrode 31.

As mentioned above, in the radical gas generation system 500 accordingto the present embodiment, the radical gas generation apparatus 100includes the plurality of discharge cells 70 and each of the dischargecells 70 has the opening 102. The plurality of radical gases G2 areconducted from the radical gas generation apparatus 100 to the processchamber apparatus 200 through the openings 102. The target object 202 isrotated. One n-phase inverter power supply device 9 outputs, to thedischarge cells 70, n-phase alternating current high voltages voltagesof different phases independent of one another, so that the amplitude ofthe alternating current voltage applied to the individual discharge cell70 varies according to the distance from the rotation center of thetarget object 202 and the density of the electric discharge energysupplied to the discharge space 40 varies accordingly.

The density of electric discharge energy varies as mentioned above, sothat the amount of radical in the radical gas G2 (the concentration ofthe radical gas) generated in the radical gas generation apparatus 100varies accordingly through the openings 102. This configurationeliminates the need for providing a plurality of alternating currenthigh voltage sources to one radical gas generation apparatus 100 anduses one n-phase inverter power supply device 9 to control the amount(concentration) of the radical gas G2 sprayed from each of the dischargecells 70. The small-footprint apparatus can perform, at a low cost, aradical gas process evenly on the target object 202 having a large area.

With reference to FIG. 2, the discharge cells 70 have the same outlineshape (specifically, the dielectrics 2 and 3 of the discharge cells 70have the same outside shape) and the openings 102 of the discharge cells70 have the same opening diameter. The amount (concentration) of theradical generated in the discharge space 40 is variably controlled to beless than 1% at most. The amount (concentration) of the radical can becontrolled according to the position of the individual discharge cell 70while the gas is sprayed through the openings 102 at approximately thesame speed.

In the control circuit 907, the PID control is performed based on thefeedback on the current value detected in each phase, regardless ofsmall changes in discharge load conditions associated with, for example,the temperature of the individual discharge cell 70, the gas flow rate,and the gas pressure. Thus, the alternating current voltage can beapplied more stably and the amount of electric power supplied to thedischarge cells 70 can be controlled.

The target object 202 is rotated. Thus, the opening diameter of theindividual opening 102 through which the radical gas G2 is sprayed canbe reduced and the speed of the radical gas G2 can be further increasedaccordingly. The radical gas G2 can reach the target object 202 in ashort time, so that the radical gas G2 is less likely to disappearbefore reaching the target object 202.

The dielectrics 2 and 3 that are located in the individual dischargecell 70 so as to face the discharge space 40 may be made ofsingle-crystal sapphire or quartz.

In the discharge space 40, a dielectric barrier discharge occurs,inflicting discharge damage to the dielectrics 2 and 3. The dielectrics2 and 3 made of single-crystal sapphire or quartz have improvedresistance properties, which can minimize the amount of particles thatare deposited on the dielectrics 2 and 3 due to the dielectric barrierdischarge.

In the radical gas generation apparatus 100, the discharge space 40needs to be placed in a high-field plasma state such that thehigh-quality radical gas G2 is generated through the use of thedielectric barrier discharge occurring in the discharge space 40. Theelectric filed in the discharge space 40 is dependent on the valueobtained by multiplying the gas pressure in the discharge space 40 bythe gap length in the discharge space. It is required that the valueobtained by “P·d(kPa·cm)” be less than or equal to a predetermined valuein order to create the high-field plasma state. P denotes the pressurein the radical gas generation apparatus 100 and d denotes the gap lengthof the individual discharge cell 70 (the distance between the firstdielectric 2 and the second dielectric 3, which is equal among thedischarge cells 70).

Assume that the same value is obtained as the product of P and d in thefollowing two cases associated with the radical gas, one case (referredto as the former case) fulfilling the condition of “atmosphericpressure+short gap length” and the other case (referred to as the lattercase) fulfilling the condition of “reduced pressure+long gap length”.One case has the advantages over the other case. That is, the lattercase has the advantages that the speed of the gas flowing through thedischarge space 40 is increased and that the gap length (the wall of adischarge surface) is extended to minimize the loss of the radical gasG2 caused by a collision of the radical gas G2 with the wall (or tominimize the breakdown of the amount of the generated radical gas (theconcentration of the generated radical gas)).

The inventors have found that it is desirable that the radical gasgeneration apparatus 100 fulfill the following conditions in order todrive the dielectric barrier discharge stably and to generate anexcellent radical gas.

The inner gas pressure P of the radical gas generation apparatus 100 isdesirably set at about 10 to 30 kPa and the gap length d of thedischarge space 40 is desirably set at about 0.3 to 3 mm such that theproduct of P and d is of the order of 0.3 to 9 (kPa·cm).

According to the above-mentioned configuration, the radical gasgeneration apparatus 100 is disposed in the process chamber apparatus200 in which the target object 202 is rotated. The radical gasgeneration apparatus 100 includes the plurality of discharge cells 70.The generation amount of the radical gas to be sprayed through theopening 102 of the individual discharge cell 70 varies according to theposition corresponding to the rotation angular speed of the targetobject 202, so that a film is deposited evenly on the target objecthaving a large area in a short time. The above-mentioned configurationis applicable to the radical gas generation system including a powersupply device. The radical gas generation apparatus 100 includes theplurality of discharge cells 70 and is disposed on the process chamberapparatus 200. The power supply device can apply a given alternatingcurrent voltage to each of the plurality of discharge cells 70.

The radical generation system that includes the power supply device andis for use in film formation has been described as one embodiment. Theabove-mentioned configuration is also applicable to other radicalgenerators and power supply devices of electric discharge generators.

EXPLANATION OF REFERENCE SIGNS

1 low voltage electrode

2 first dielectric

3 second dielectric

4 spacer

5 high voltage electrode block

9 n-phase inverter power supply device

31 high voltage electrode

40 discharge space

70 discharge cell

101 source gas supply unit

102 opening

100 radical gas generation apparatus

200 process chamber apparatus

201 table

202 target object

203 gas outlet

300 vacuum pump

500 radical gas generation system

901 rectifier circuit

902 inverter element

903 current-limiting reactor

904 transformer

905 gate circuit

906 current detector

907 control circuit

G1 source gas

G2 radical gas

1. An electric discharge generator and a power supply device of electricdischarge generator comprising: a radical gas generation apparatus thatgenerates a radical gas from a source gas using a dielectric barrierdischarge; a process chamber apparatus that is connected to said radicalgas generation apparatus, accommodates a target object, and performs, onsaid target object, a process in which said radical gas is used; and apower supply device that applies an alternating current voltage to saidradical gas generation apparatus, wherein said process chamber apparatusincludes a table on which said target object is placed, said tablecausing said target object to rotate, said radical gas generationapparatus includes: a plurality of discharge cells that cause saiddielectric barrier discharge; and a source gas supply unit that suppliessaid radical gas generation apparatus with said source gas, each of saidplurality of discharge cells includes: a first electrode portionincluding a first electrode member; a second electrode portion that isopposed to said first electrode portion and includes a second electrodemember; and an opening connected to the inside of said process chamberand facing said target object placed on said table, said radical gasgenerated from said source gas using said dielectric barrier dischargebeing output through said opening, and said power supply device includesa power supply circuit configuration that receives input of onealternating current voltage and controls output of n-phase alternatingcurrent voltages, applies each of said n-phase alternating currentvoltages to corresponding one of said plurality of discharge cells, andvariably controls, according to positions of said plurality of dischargecells, said alternating current voltages to be applied to said pluralityof discharge cells, where n represents the number of said plurality ofdischarge cells.
 2. The electric discharge generator and the powersupply device of electric discharge generator according to claim 1,wherein said power supply circuit configuration includes n-phaseinverters and n-phase transformers, each of said n-phase alternatingcurrent voltages is applied to corresponding one of said plurality ofdischarge cells, and of said plurality of discharge cells, a dischargecell located farther from a center position of the rotation of saidtarget object in a plan view is subjected to application of a higheralternating current voltage.
 3. The electric discharge generator and thepower supply device of electric discharge generator according to claim2, wherein said power supply device detects a direct current dividedinto different phases and performs a PID control on a pulse width or apulse cycle of each of said n-phase inverters based on detectionresults.
 4. The electric discharge generator and the power supply deviceof electric discharge generator according to claim 1, wherein each ofsaid plurality of discharge cells further includes a dielectric thatfaces a discharge space in which said dielectric barrier dischargeoccurs, and said dielectric is made of single sapphire or quartz.
 5. Theelectric discharge generator and the power supply device of electricdischarge generator according to claim 1, wherein said radical gasgeneration apparatus has an internal gas pressure of 10 to 30 kPa, andthe distance between said first electrode portion and said secondelectrode portion is set at 0.3 to 3 mm.
 6. The electric dischargegenerator and the power supply device of electric discharge generatoraccording to claim 1, wherein said source gas comprises a nitrogen gas,said radical gas generation apparatus generates, as said radical gas, anitrogen radical gas from said nitrogen gas, and said process chamberapparatus forms a nitride film on said target object using said nitrogenradical gas.
 7. The electric discharge generator and the power supplydevice of electric discharge generator according to claim 1, whereinsaid source gas comprises an ozone gas or an oxygen gas, said radicalgas generation apparatus generates, as said radical gas, an oxygenradical gas from said ozone gas or said oxygen gas, and said processchamber apparatus forms an oxide film on said target object using saidoxygen radical gas.
 8. The electric discharge generator and the powersupply device of electric discharge generator according to claim 1,wherein said source gas comprises a hydrogen gas or water vapor, saidradical gas generation apparatus generates, as said radical gas, ahydrogen radical gas or hydroxyl (OH) radical gas from said hydrogen gasor said water vapor, and said process chamber apparatus forms a metalfilm with enhanced hydrogen bonding on said target object using saidhydrogen radical gas or said OH radical gas.